The invention relates to the art of semiconductor manufacture. It finds specific application for fuses within an integrated circuit and will be described with particular reference thereto. However, it is to be appreciated that the present invention is also amenable to PROM-type devices, trimming resistors and other like devices.
Fuses have long been important circuit elements. While fuses are generally used for circuit protection and fire prevention, in integrated circuits they are also used as a means of calibration, programming and providing data security. For example, fuses can be used for trimming or calibrating certain parameters in a circuit, or for recording information by selectively blowing fuse elements in an array, or for preventing information stored in a memory device from being accessed. Whether the fuse exists for circuit protection or to achieve certain operating parameters the fuses are designed to change state under certain conditions. Indeed, one way to change state is a to blow a fuse. This is accomplished by applying a sufficiently high current through the fuse. The heating that results causes the conductor to melt or vaporize. In this way, the fuse is transformed from its conductive state to a blown, or open circuit state.
The conductors used to fabricate fuses on integrated circuits are made of layers of conductive metal, typically aluminum or aluminum compound. For reasons unrelated to fusing, the aluminum layer is deposited over a barrier layer typically comprising titanium and/or a titanium compound. Unfortunately, the addition of titanium has an adverse effect on fuse reliability. The adverse effect is caused by the high melting point of titanium as compared to the aluminum bulk conductor layer. Thus, when current levels are applied to the metal stack which should effect a blown fuse, sometimes portions of the barrier layer remain. This remaining portion of the barrier provides a conductive path around the `blown` fuse. In other words, current levels that do melt the bulk conductor sometimes do not completely melt the barrier layer. This partial path undesirably allows a current path, defeating the intended open circuit.
Accordingly, it is desirable to provide a technique for manufacturing a more reliable fuse, using existing methods of applying the metal stack.
The present invention contemplates a new and improved method and apparatus fuse overcomes the above-referenced problems and others.